Ignore duplicate path/field/token links.

This is occasionally important when dealing with arrays in metadata,
where each element is processed separately and not subject to token
deduplication; as a result, we end up attempting to insert duplicate
path/field/token links. By ignoring hese, we ensure that the index
builds, and we also save space by trimming out duplicate tokens.

src/sqlite/createTables.js

@@ -15,7 +15,7 @@ export function createTables(db) {
     db.prepare("CREATE INDEX index_fields ON fields(field)").run();
 
     db.prepare(`CREATE TABLE links (pid INTEGER NOT NULL, fid INTEGER NOT NULL, tid INTEGER NOT NULL,
-    UNIQUE(pid, fid, tid),
+    UNIQUE(pid, fid, tid) ON CONFLICT IGNORE,
     FOREIGN KEY(pid) REFERENCES paths(pid) ON DELETE CASCADE)`).run();
     db.prepare("CREATE INDEX index_links ON links(tid, fid)").run();
     return;